1. Field of the Invention
This invention relates to a semiconductor wafer cassette and wafer transfer system for the temporary storage and transfer of semiconductor wafers during the manufacturing process; and more particularly, to a semiconductor wafer cassette apparatus and associated transfer system which is capable of directly loading and unloading wafers into the cassette from different sides using a first robot handling means having a wafer transfer blade movable along a first extension path and a second robot handling means having a second wafer transfer blade movable along a second extension path intersecting the first extension path at an acute angle and at a predetermined point concurrent with the cassette's wafer position centerline.
2. Description of the Prior Art
In the manufacture of semiconductor wafers, a plurality of wafers are temporarily stored and transferred between manufacturing and processing apparatus locations in factory cassettes. At the processing apparatus location, the factory cassette is either manually or automatically loaded into a loadlock chamber of the processing apparatus wherefrom the wafers may be unloaded for processing, or a factory robot unloads the wafers individually from the factory cassette and loads them into a fixed temporary storage cassette positioned in the loadlock chamber.
In the former case, where the factory cassette is manually loaded, the cassette is typically accessible from one side only and is oriented so that the system robot can access the wafer directly along an extension path directed perpendicular to the accessible side of the cassette. In the latter case, where a factory robot loads and unloads individual wafers between a factory cassette and a fixed cassette positioned in the loadlock chamber, the cassette is accessible from different sides, i.e., it is a "pass-through" cassette. As such, the pass-through cassette can be directly accessed by both the factory robot and the system robot if both robots are disposed in a position such that the extension path of each robot arm is along a common axis directed perpendicular to the accessible sides of the pass-through cassette.
The pass-through type of cassette is preferred over the cassettes having only one accessible side because it enables efficient robotic wafer handling, both inside and outside of the processing apparatus.
Also preferred for processing efficiency is a processing apparatus having a plurality of loadlock chambers for accommodating simultaneous loading/unloading operations by both the factory robot and the system robot. In this case, multiple loadlock chambers are positioned about a generally cylindrical, (multi-faced) wafer transfer chamber having a "simple" R-theta type robot (i.e., a robot having two degrees of freedom, one in extension/retraction and one in rotation) disposed therein. A simple R-theta robot is preferred so that it can rotate and load/unload wafers from any processing chamber disposed about the periphery of the transfer chamber.
However, to incorporate a pass-through cassette with this type of multiple loadlock system where the load/unload path is perpendicular to the accessible side of the cassette, requires a more sophisticated system robot having a particular type of articulated arm so that it can move laterally to position the robot arm along the path perpendicular to the accessible side of the pass-through cassette and extend/retract for loading/unloading of the wafers. Such a robot is more expensive, more complicated and less reliable than a simple R-theta robot that does not have this type of articulated arm. Therefore, a need has arisen in the art so that a simple R-theta robot can be used with a pass-through cassette disposed within multiple loadlock chambers.
One solution to this problem is to provide a means for orienting the pass-through cassette once loaded, i.e., rotate the cassette, so that it can be accessed on one side along the extension path of the R-theta robot and on the other side along the extension path of the factory robot. However, providing such an orientation means adds undesirable complexity and cost to the system.
Thus, it would be desirable to provide a semiconductor wafer transfer system which includes a pass-through-type wafer cassette disposed within a plurality of loadlock chambers positioned about the periphery of a generally circular transfer chamber having an R-theta robot(without articulated arm), and which can be directly loaded/unloaded from one side by a factory robot and from a different side by a system R-theta robot, the two robots having extension paths intersecting at an acute angle.